The clinical study of neurogenetic diseases provides opportunities for developing improved diagnostic technology and innovative treatment modalities. A number of novel neurogenetic diseases have been identified by studies performed under this project. New clinical phenotypes have been recognized including biopterin deficiency presenting as familial dystonia, a severe variant of cholesterol ester storage disease presenting with advanced liver disease, and a novel lipid storage disorder caused by failure to up-regulate intracellular cholesterol processing enzymes. The etiopathogenesis of von Hippel-Lindau disease is under intensive investigation. Biopterin supplementation has been examined in diurnally variant dystonia patients with Types C and D Niemann-Pick disease.